Recently, IRS has been considered as a promising new technology for the next-generation wireless communications, which can reconfigure the wireless propagation environment via controlling reflection with software [1]}. Specifically, an IRS composes a large number of low-cost passive reflecting elements, each of which can induce a phase change to the incident signal independently. By smartly adjusting the phase shift of the reflecting elements, the IRS reflected signals and the signals from other paths can be combined constructively to enhance the desired signal power or destructively to suppress undesired signals such as co-channel interference, which thus significantly improves the communication performance. A typical IRS-aided MISO multi-user secure system is shown in Figure. REF . The introduction of IRS in the system can increase the achievable rate of legitimate users (i.e., Bobs) while suppressing the achievable rate of illegal users (i.e., Eves), ultimately improving the security performance of the system. Hence, IRS can be used for strengthening the system security under the wiretap channel, especially when the channel of the eavesdropping communication link is stronger than that of the legitimate link.
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